Multi-discrete-phase Fresnel elements have been proposed for optical applications. See Swanson et al., "Infrared Applications of Diffractive Optical Elements," Holographic Optics: Design and Applications, SPIE Vol. 883, 1988, pp 155-162. However, there still is a need for an economical and reliable process for manufacturing optical and acoustical lenses of that type in compliance with relatively exacting design specifications.